1. Field of the Invention
This invention relates generally to T1/E1 type communications. More particularly, it relates to the implementation of a digital adaptive equalizer for a T1 or E1 long haul transceiver.
2. Background of Related Art
Telecommunications and more recently data communications commonly utilize T1 or E1 rate long haul transceivers for transmitting large amounts of data. A T1 type signal (1.544 Mb/s) is a standard 24 channel digital communication standard commonly used in North America. An E1 type signal (2.048 Mb/s) is a standard 30 voice channel or 32 payload channel digital communication standard commonly used in Europe. However, because of the similarities in the data structure and physical layer characteristics of T1 and E1 lines, many commercial components are capable of supporting either a T1 or an E1 standard, often with a bit setting or swap of a termination impedance.
As is known, data transmissions suffer dispersion and other debilitating degradations during transmission, particularly when transmitted over a twisted pair and/or cable.
In particular, FIG. 9 depicts the affects of a transmission path 910 between a T1/E1 transmitter 902 and a complementary T1/E1 receiver 904. The transmission path 910 (e.g., twisted pair, coaxial cable, etc.) typically causes dispersion, attenuation, and/or other distortion with respect to a frequency domain as depicted in FIG. 9, which is ideally compensated by an analog equalizer 912 in the T1/E1 receiver 904.
Conventional T1 or E1 equalizers 912 are analog devices included in the T1/E1 receiver 904 which are specifically adapted and designed to cancel the affects of the known transmission path 910 (e.g., twisted pair, coaxial cable, etc.) and a known length of that transmission path 910, by equalizing the received signal before processing. Thus, a conventional analog equalizer is chosen or designed based on the specific type of cable used, and on the specific length of the cable. Even given a same type cable, generally speaking the longer the cable, the more affected the received T1/E1 signal is by transmission through the path 910.
Conventional analog devices are typically designed with the specific cable type and sometimes even the length of the cable in mind. Thus, as cable length changes and/or as cable types change, conventional analog T1/E1 equalizers require physical changes to the circuit board containing the T1/E1 long haul transceiver to allow proper equalization of the received T1 or E1 signal. This poses delays and reliability issues when changes to a system are incurred, e.g., when increasing or decreasing the length of a T1/E1 cable.
There is a need for a more flexible T1/E1 equalizer which adapts to changes in T1/E1 cable type and/or length without requiring physical hardware changes to the receiving T1/E1 long haul device.